Resistance unit.



E. THoM'soN.

RESISTANCE UNIT.

APPLICATION FILED DEO.2, 1904.

Patented Jan. 11,1910.

Fig. 5.

Inventor n Elihu Thomson, b5 MMM Dtt'g.

Witnesses:

UNITED STAT-Es PATENT oEEicE.

ELIHU THOMSON, 0F SWAMPSCOTT, MASSACHUSETTS, ASSIGNOR TO GENERALELECTRIC COMPANY, A CORPORATION 0F NEW YORK.

RESISTANCE UNIT.

Specification of Letters Patent.

Patented Jan. 11, 1910.

To all whom 'it may concern:

Be it known that I, ELIHU THOMSON, a citizen of the United States,residin at Swampscott, county of Essex, State of as` saehusetts, haveinvented certain new and useful Improvements in Resistance Units, ofwhich the following is a specification.

This invention relates to an improved form of resistance unit. Whilethis unit may be used in a great variety of Ways it is believed to beparticularly valuable when used for automatic current control or whenused in connection with circuits subjected to sudden and heavy rushes ofcurrent, as for instance lightning arrester and similar circuits.

In the drawing, Figure 1 is a cross-section of one form of my improvedresistance unit showing the granulated resistance material retained inthe refractory tube; Fig. 2 is a plan view of the same; Fig. 8 is aresistance unit of cast silicon provided with suitable conductingterminals; Fig. 4 shows a refractory cage for su porting the granulatedresistance material) in place; and Fig. 5 is a cross-section on the line5 5 of Fig. 4.

In Figs. 1 and 2 the non-conducting base 1 of porcelain or othersuitable non-conducting material has secured rigidly thereto themetallic terminal blocks 2 and 3, carrying the binding posts 4 and 5 bywhich the unit may be connected in circuit. The non-conductin cylinder 6incloses the resistance material g, and holds it in place. This tube 6consists preferably of a rough uartz cylinder such as may be made by meting granulated quartz arounda heated carbon tube or by other Well knownprocesses. A tube of this material has the advantage that it does notbecome a conductor, except very slightly, even at very hightemperatures, and furthermore, does not deteriorate when exposed to theair at these hi h temperatures. The resistance material ma consist ofuncombined silicon in granu ar form. This element has a high specificresistance, a high fusing point and a suitable temperature coecient, andfurthermore is not readily oxidized at high temperatures; all of whichcharacteristics make it admirably adapted for use as a resistancematerial for carrying sudden and heavy discharges. The resistancematerial 7 is preferably packed in a tube 6, and held firmly in place bythe two metallic electrodes Sand 9 supported respectively in theterminal blocks 2 and 23 and pressed toward each other by the coilsprings 10 and 1l, or other suitable spring mechanism.

At very high temperaturesI the clement silicon may be fused and cast inthe form of a prismatic or cylindrical unit as shown in Fig. 3, in which12 is a silicon cylinder screwthreaded at each end and provided withmetallic caps 13 and 14 of good conducting material to which the circuitmay be connected. If desired, the terminals 12 and 14 may be castdirectly to the ends of thev silicon rod instead of being screw-threadedthereto.

In Figs. 4 and 5 is shown a modified form of resistance unit, similar tothe form shown in Fig. 1 except that the quartz tube is replaced by acage of refractory material. This cage consists of longitudinal bars 15transversely notched to receive the rings 16, thus forming a cylindricalcage within which the resistance material 7is securely held underpressure by the metal electrodes 8 and 9.

The resistance of the units shown in Figs. 1 and 4 may be readilycontrolled by varying the size of the granulated particles, as well asby increasing the length and crosssection of the unit. As the specificresistance of the element silicon is nearly twice that of ordinarycarbon, and furthermore as silicon unlike carbon is able to stand a redheat without oxidation, the units herein described are particularlyvaluable for use in connection with lightning arresters in place of theordinary cylindrical resistance units or carbon or graphite.

Aside from the superiority of these resistance units for controllingsudden and heavy rushes of current they possess certain other valuablecharacteristics because of the peculiar temperature-resistance coeicientof the element silicon. At normal temperatuies cast silicon has a nearlyconstant resistance so that upon an increase in temperature up to a redheat the electrical resistance increases only slightly. This variationis very much less than is ordinarily found in the metallic elements andabove a. red heat the resistance increases somewhat with temperatureshowing a positive temperature coefficient. This temperature coeiiicientis not, however, a constant for all higher degrees of heat and'at atemperature approximating that of 'melting silver the temperatureeoeiicient reverses u sign so that a further heating causes an actualand rather ra id reduction in the resistance of the unit. his negativetemperature coefficient makes the resistance units herein describedsuitable for automatic motor starting rheostats and for other purposesWhere it is desirable that the resistance should automatically decreaseas the impressed voltage or the current flow increases. The change intemperature coeicient from a slight or positive value to a high negativevalue thus successively increasing and decreasing the resistance makesthe silicon resistance units available for automatic protectors andregulators for a great variety of purposes, such for instance asautomatic cut-outs for mercury va or lamps and other translating devicesused in series circuits, or as a means for automatically grounding acircuit to static or other abnormal voltage.

What I claim as new, and desire to secure by Letters Patent of theUnited States, is,-

1. In a resistance unit, a resistance material consisting of granulatedsilicon, and

means for retaining said material in place under pressure.

2. In a resistance unit, conducting terminals and a resistance materialbetween said terminals, said resistance material consisting ofgranulated silicon.

3. A resistance unit comprising a quartz tube, a, resistance materialconsisting of granulated silicon packed Within said tube, conductingterminals in contact with said material, and means'for retaining saidresistance material under pressure.

4. A resistance unit comprising a non-conducting tube, a resistancematerial in granular form packed Within said tube, said resistancematerial consisting of an incombustible substance having a negativetemperature-resistance coefficient at certain temperatures, conductingterminals in contact with said material, and means for retaining saidmaterial under yieldin ressure.

In Witness Whereo fhave hereunto set my hand this 14th day of November,1904.

ELIHU THOMSON. Witnesses:

JOHN A. MCMANUS, Jr., DUGALD MCK. MCKILLOP.

